1. Field of the Invention
Embodiments of the present invention relate to electronic testing circuitry. More particularly, embodiments of the present invention relate to electronic circuitry to test a high speed data bus.
2. Description of the Related Art
Aircraft and other vehicles often include data communication systems that transmit electronic data over a data bus. For example, components in one location of the aircraft, such as cockpit control systems, may communicate with components in another location, such as engine or rudder controllers. Ground-based vehicles, such as military tanks, and marine vessels, such as submarines, may include similar types of data communication systems. The data bus used in these types of systems is typically implemented utilizing the MIL-STD-1553 standard for data buses. The MIL-STD-1553 standard is published by the United States Department of Defense and specifies the requirements for the architecture of the data bus as well as the physical connection between components. Other buses, such as the controller-area network (CAN) bus for the automotive industry, may include similar features.
The MIL-STD-1553 data bus is a serial communication bus that operates at 1 megahertz (MHz) and includes a main trunk to which each component is connected. The MIL-STD-1553 data bus requires a bus controller, which is connected to the main trunk, to manage communication between the components. A component generally checks with the bus controller before communicating with another component over the data bus. The main trunk may be a two-line bus which is physically implemented with a two-wire cable, such as a coaxial cable or a twisted pair cable. Each end of the main trunk is terminated with an impedance, known as a terminator, between the two lines. Each component and the bus controller are connected to the main trunk through a stub coupler. The stub coupler is configured to include a transformer whose primary is coupled to one of the lines of the data bus and whose secondary couples to the component or the bus controller, usually through another two-wire cable. Thus, the MIL-STD-1553 data bus typically includes at least the following: a first terminator connected to a first stub coupler, which is connected to a component or a bus controller through a first cable. Also connected to the first stub coupler is a second cable that connects to a second stub coupler, to which is connected the component or the bus controller through a third cable. If that is the end of the main trunk, then a second terminator may also be connected to the second stub coupler.
The MIL-STD-1553 data bus, to which a large number of components may be connected, may experience a certain amount of signal attenuation because the data communicated from one component to another may travel through a large number of cables and stub couplers. Furthermore, it is possible for the cables or stub couplers to become misconnected such that the two lines of a portion of the data bus have the wrong polarity. These same issues may affect other similar data buses.